1. Field of the Invention
This invention relates to apparatus and a method of operating the same for servicing a steam generator and, more particularly, to determinining the identity and angular position of an end effector cantilevered from a servicing machine and to operating the machine to align the end effector with a selected portion of the steam generator tubesheet, taking into account the offset of the end effector.
2. Description of the Prior Art
Commonly owned U.S. Pat. No. 4,205,940 discloses a machine for servicing the tubesheet of a steam generator in a pressurized water reactor nuclear powered electric generating system, and U.S. patent application Ser. No. 952,431 filed Oct. 18, 1978 discloses a method of operating the machine. That servicing machine includes an arm pivoted to move in a plane parallel to and underneath the semicircular hole array in one-half of a steam generator tubesheet. A carriage mounted for reciprocal movement along the arm is provided with a platform which can be raised toward the tubesheet. In order to carry out selected operations on the tubesheet, various end effectors may be mounted on the platform. Due to the constraints imposed by the shape of the channel head below the tubesheet and the proximity of some of the holes in the array to the walls of the channel head, it is necessary that the end effectors be mounted on cantilevered arms and that the cantilevered arms be mounted at different angles on the platform in order to reach all of the holes in the array with the different end effectors. In some instances, cantilevered arms of more than one length are required for one type of end effectors in order that the desired operations can be performed at each of the holes in the array.
In order to change the end effectors or to adjust the angular position of the cantilevered arms on the platform of the servicing machine, the machine arm is pivoted out of the plane parallel to the tubesheet and is angularly aligned with a manway in the channel head where a technician can manually make the required changes. Since this process is time consuming and exposes the technician to radioactivity present in the channel head, an automatic slewing table was developed for use with some of the end effectors. This device, which permits the changes in angular position of the cantilevered arm to be made remotely, is described in U.S. patent application Ser. No. 896,530 filed Apr. 14, 1978 U.S. Pat. No. 4,200,424 and a method for operating it is disclosed in U.S. patent application Ser. No. 974,159 filed Dec. 28, 1978.
In performing the various operations on the tubesheet, the offset of the end effector produced by the length of the cantilevered arm and its angular position on the platform must be taken into account. When the angular position of the arm is set manually by a technician, both this angle and the radial distant of the end effector from the pivot point on the platform must be manually supplied to the servicing machine control system. When the automatic slewing table is used, the angular position of the cantilevered end effector support is automatically supplied to the control system as an analog signal by a feedback sensor; however, it is still necessary to manually identify to the control system the radial offset of the end effector as mounted on the particular cantilevered arm. It is essential that the precise offset, both radially and angularly, of the end effector be supplied to the servicing machine control system to preclude damage to the machine or steam generator such as by interference between portions of the machine and the steam generator or by performing an operation, like drilling a hole, at the wrong location. It is also essential that the correct end effector be mounted on the platform for the operation to be performed by the machine.
It is a primary object of this invention to provide apparatus and a method for accurately identifying to a steam generator servicing machine the end effector carried by an arm cantilevered from the machine and the angular position of the cantilevered arm on the machine.
It is also an object of the invention to utilize this information to control the operation of the servicing machine.